I have checked the inside of my washer and can't find anything. It smells like mildew. Any ideas?
You are unlikely to see anything unless the machine is disassembled. Residue collects on outside of the inner basket and on the outer tub. Run the HOTTEST wash you can get with a good dose (1 measured cup, maybe 2 cups if it's a deep-fill agitator toploader) of a dishwasher detergent containing enzymes. Then repeat with 1 cup (or 2) of LemiShine. If the machine is a agitator toploader, set the highest water level available, then add 1 quart to 1/2 gallon or so more hot water after it finishes filling to raise the level slightly higher, above the residue line in the tub. Adding water isn't necessary if it's a frontloader.
Good advice above. Also, if you do a search of this forum you will find multiple posts on this same subject. The cure seems to be regular hot washes, leaving the washer door open, and powder detergent.